A team of researchers from the Georgia Institute of Technology have developed a self-charging power cell that is able to directly convert mechanical energy into chemical energy. The cell then stores the power until it is released as electrical current. The all-in-one piezoelectric power cell essentially eliminates the need to convert mechanical energy to electrical energy for charging a battery, as its new hybrid generator/storage capability utilizes mechanical energy more efficiently than systems which use separate generators and batteries.

The cell is based on a piezoelectric membrane – when mechanical pressure is applied to it lithium ions are driven from one side of the cell to the other. After the lithium ions are driven through the polarized membrane they are directly stored as chemical energy using an electrochemical process.

The pressure needed to drive the membrane can be something as simple as the compressive force of a shoe heel, so a person could easily power the cell just by walking. So far, the team’s power cell generates enough current to power a small calculator, but they expect to increase its capacity in the near future.

“People are accustomed to considering electrical generation and storage as two separate operations done in two separate units,” said Zhong Lin Wang, a Regents professor at the School of Materials Science and Engineering at the Georgia Institute of Technology. “We have put them together in a single hybrid unit to create a self-charging power cell, demonstrating a new technique for charge conversion and storage in one integrated unit.”

So far, Wang and his research team have built and tested more than 500 of the power cells. They believe that the generator/storage cell will be as much as five times more efficient at converting mechanical energy to chemical energy than a two-cell generator/storage system.

“(By improving) the packaging materials, we anticipate improving the overall efficiency,” he said. “The amount of energy actually going into the cell is relatively small at this stage because so much of it is consumed by the shell.”

“One day we could have a power package ready to use that takes advantage of this hybrid approach,” Wang added. “Almost anything that involves mechanical action could provide the strain needed for charging. People walking could be generating electricity as they move.”

The team’s research was reported Aug. 9, 2012 in the journal Nano Letters. The project has received funding from the Defense Advanced Research Projects Agency (DARPA), the U.S. Air Force, the U.S. Department of Energy, the National Science Foundation, and the Knowledge Innovation Program of the Chinese Academy of Sciences.